Stimulation of tissue in humans and other animals is used in a number of clinical applications as well as in clinical and general biological research. In particular, stimulation of neural tissue has been used in the treatment of various diseases including Parkinson's disease, depression, and intractable pain. The stimulation may be applied invasively, e.g., by performing surgery to remove a portion of the skull and implanting electrodes in a specific location within brain tissue, or non-invasively, e.g., transcranial direct current stimulation and transcranial magnetic stimulation.